Lasers:

This can be done by heating the build chamber/box to 10 degrees below its Tg (glass transition) temperature and using the laser to increase the temperature over Tg to it's melting point. The surface

For laser, a 5 watt laser can be used to melt the nylon. Heating the build volume with heated plates from all sides and above via a heat lamp the nylon could be brought close to its melting point. Then, the laser can be used to raise it over this point, causing it to melt. This also would help combat warping of the parts, which in FDM printing nylon is notorious for.

The Scanner system: For this typically a galvanometer is used. They are expensive. The laser could be moved using a common xy mechanism (such as corexy) or by scanning the beam across the build platform by means of a galvanometer. A low cost galvanometer system could be implemented as below: